Phosphoinositide 3-kinases (PI3Ks) are heterodimeric enzymes that utilize both lipid and protein kinase activity to regulate numerous lipid signaling pathways that are responsible for coordinating a broad range of cellular activities including cell survival, proliferation, and differentiation as well as inflammatory responses. The critical role of PI3Ks in these myriad important cellular processes make them a very attractive target for pharmaceutical intervention. The class of PI3Ks relevant to this disclosure catalyze the phosphorylation of phosphatilyl-inositol (4,5)-bisphosphate (PtIns(4,5)P2 or PIP2) on the 3-hydroxyl group of the inositol ring to produce the signaling molecule phosphatilyl-inositol (3,4,5)-triphosphate (PtIns(3,4,5)P3 or PIP3).
After extensive studies on the physiological role of the PI3K delta isoform in disease, PI3K delta is implicated in a large number of immunological, inflammatory and cell regulation dysfunctions. Initial studies have focused its role in immune and inflammatory pathologies. PI3K delta plays a significant role in the development, differentiation, proliferation and effector function of B-cells and T-cells. PI3K delta knock-in mice (D910A/D910A) have shown impaired or diminished proliferative T-cell responses and chemokine production when stimulated with T-cell receptor specific antigens. Moreover, these PI3K delta expressing animals demonstrate poor T-cell independent antibody responses concomitant with poor development of germinal centers in the spleen, lymph nodes and Peyer's patches and lymphoid hyperplasia after immunization. Inhibition of PI3K delta function also leads to dysfunctional homing by T-cells to sites of inflammation. PI3K delta activity has also been implicated in Treg cell control. PI3K delta(D910A/D910A) mice have Treg cells that fail to: 1.) suppress the proliferation of CD4+ CD25− T-cells in vitro as well as Treg cells from wild-type animals; 2.) produce detectable levels of the anti-inflammatory cytokine IL-10; and 3.) protect against experimental colitis.
The effects of PI3K delta on B-cells are no less significant. Mice lacking p110 delta catalytic activity have reduced numbers of B1 and marginal zone (MZ) B cells, reduced levels of serum immunoglogulins, and respond poorly to immunization with a thymus-independent antigen and are defective in their primary and secondary responses to thymus dependent antigens. Inhibition of PI3K delta via use of PI3K delta selective inhibitors have shown inhibition of B-cell receptor-induced B cell proliferation, and increased class-switch recombination, and defects in B-cell chemotaxis.
Experimental observations that PI3K delta may play a significant role in mediating the proinflammatory role of non-lymphoid hematopoetic cells have come from studies involving hematopoietic immune cells such as neutrophils, macrophages, dendritic cells, mast cells and eosinophils. For example, PI3K delta is required for neutrophil spreading and polarization, regulation of neutrophil migration, mast cell degranulation and among many others. A review of the important roles of PI3K delta in innate and adaptive immune responses, has generated intense investigation of the role of PI3K delta in immune diseases such as allergy, asthma, autoimmune diseases, and inflammation.
While a significant portion of the published scientific literature has focused on immune diseases, such as inflammation, autoimmune disease and the like, an attractive and productive area for investigation includes the role of PI3K delta in cancer. Experimental models have already provided for putative roles of PI3K alpha and PI3K beta in malignant cellular processes, including: (i) overexpression is capable of inducing transformation in experimental models; (ii) involvement in cell proliferation and tumor angiogenesis; (iii) involvement in Ras-induces transformation and oncogenesis (iv) activating mutations in the helical and kinase domains in breast and colon tumors; and (v) transformation induced by PTEN inactivation in vitro and in vivo.
As with PI3K alpha and PI3K beta, PI3K delta also induces oncogenic transformation in culture. When PI3K delta is introduced into chicken embryo fibroblasts (CEFs) with an avian retroviral vector, distinct foci form within ten days. When D910A kinase inactive PI3K delta is introduced into CEFs, no focus formation is observed indicating that transformation requires an active catalytic domain. As was observed for an oncogenic variant of PI3K alpha (H1047R), CEFs infected with PI3K delta showed constitutive activation of Akt at a level similar to PI3K alpha, even in serum starved conditions. For at least the reasons provided above, there is a need for selective PI3K delta inhibitors that can be used to prevent, treat or ameliorate PI3K delta mediated diseases, particularly in the fields of cancer, inflammation and autoimmune diseases.